My twenty year old headset had started to fail so I decided to try the Bose A20 headset to see if the noise canceling was worth the high cost. But I wanted to make an objective evaluation. To that end I assembled some test equipment. This started with a digital sound level meter to accurately measure the ambient sound in the cockpit during cruise flight. Next I downloaded a decibel meter app for my iPhone 7. To get a sound reading from inside the headset I utilized the Apple miniature headset (EarPods with Lightning Connector) that came with the phone. The microphone on this mini headset is very small and is situated under the roughened area of plastic between the + and – symbols of the headset volume controls. Before flight, I used medical tape to attach and hold the microphone of the mini headset at the center of my ear with the microphone facing outward towards the center of the aircup of the A20 headset. I also wore my Air Force style glasses (with bayonet temples) and a baseball cap which is my norm for general aviation flying. There certainly is sound leakage getting through from these but I wanted to get an objective reading for my typical flying arrangement. In the settings of both the digital sound lever meter and the iPhone app, I choose to use a weighting level of A which most closely corresponds to the human hearing range.
I choose three aircraft that I fly regularly to do measurements in, a 150 hp Citabria, a 180hp Cessna 172RG and an Airbus A-320. First I took sound level readings in the cockpit during cruise flight with the Bose A20 headset momentarily off my head to calibrate the decibel meter app on my iPhone to equal the sound level readings on the digital sound level meter. (The app had an adjustment scale for this in settings.) Now that I had an accurate phone app sound level reading, I put the Bose A20 headset on first without noise cancelation and then with.
In the Citabria, the sound level was a very high 100 dB in cruise flight. Without noise cancelation, this was reduced to 97-98 dB. According to the website dangerousdecibels dot com, a 97 dB level of sound can result in hearing damage within only 30 minutes of exposure. Next I turned on the A20 noise cancelation and found that the sound level inside the headset was reduced to 82 dB. At this level, according to the website, there is no risk of hearing damage.
In the Cessna 172RG, the sound level was 95 dB in cruise flight. Test results were much the same, without noise cancelation sound was reduced to 92 dB and with noise cancelation down to 77 dB.
Finally in the A-320, the cruise sound level was only 82 dB to start with so there is no real risk of hearing damage. The Bose A20 results in the A-320 were a reduction to 79 dB without noise canceling and down to 66 dB with. But since there isn’t a risk of hearing damage to begin with, I wouldn’t go to the effort of bringing a headset with me for flying this aircraft.
On a side note, I conducted similar tests on a brand new David Clark H10-13.4 headset. The sound level reduction in the Citabria was from 100 dB to 90 dB and from 95 dB to 85 dB in the C-172RG. Keep in mind that I was wearing a pair of glasses and a baseball cap so there was sound leakage from those.
A few observations, the Bose A20 does a great job of reducing sound when its noise canceling is working but if it isn’t working, there is just not much passive noise canceling there to prevent hearing damage in very loud aircraft. The Bose A20 does a very good job of making the radios easier to hear. ATC never sounded so crisp and clear than when I was wearing the A20 with the noise canceling. On the other side of the coin, I noticed that during early takeoff in the Citabria the Bose A20 had a tough time keeping up with the changing sound and did let through a spike of high sound that actually kind of hurt my ears but only for a moment. Also on one day in which I wore the Bose A20 headset for an hour and half flight in the Citabria, in continuous noise canceling mode, after getting home and sitting in a quiet room I experienced a faint, high pitched ringing in my ears. Perhaps there’s a high frequency sound level that the A20 doesn’t work as well with in the Citabria. I’m not sure. I did not experience this after flying in the C-172RG. But on taxi in after the flight in the C-172RG, I did notice that the Bose was having some trouble keeping up with the very low frequency sound of the 180HP engine at idle.
All in all I think the Bose A20 is an excellent headset. But if you are flying a very loud aircraft, I would definitely recommend carrying a spare set of batteries and/or earplugs to protect yourself with in case the noise canceling feature stops working.